Substances for producing crystalline heat-resistant coatings and fused layers



Unitcd States Patent 3,380,838 SUBSTANCES FOR PRODUCING CRYSTALLINE HEAT RESISTANT COATINGS AND FUSE!) LAYERS Werner Sack, Mainz, Germany, assignor to Jenaer Glaswerk Schott & Gen., Mainz, Germany, a corporation of Germany No Drawing. Filed July 30, 1964, Ser. No. 386,373 Claims priority, applicatitznlgGcfrmany, Aug. 6, 1963,

Clm ms. (Ci. 10639) ABSTRACT OF THE DISCLOSURE An MgOA1 O -SiO glass powder and MgO mixture or/and Li O+ Al O additions thereto, which is heated and sintered to produce by chemical reaction crystalline heat resistant coatings.

The invention relates to substances for producing crystalline, heat resistant coatings and fused layers and to a method of preparing such substances.

A method of producing crystalline sinter bodies is known in which inorganic compounds are added to a silicate glass powder, the mixture is heated and sintered and the sinter temperature is kept constant for a longer period of time during which the components of the mixture are brought to reaction and devitrification.

It has also been proposed heretofore to add magnesium oxide as an inorganic compound.

In accordance with these two known methods articles are produced which predominantly contain cordierite and/ or anorthite and/or spinel and/ or forsterite.

It has been discovered that the powder mixtures specified in the known methods can be used for producing crystalline and heat resistant sealing or fusing layers and coatings for quartz bodies, quartz glass, porcelain, ceramics, metals and metal alloys.

The invention resides in the further development of known glass powder mixtures and their range of application and comprises a high-alumina glass powder of the following composition:

Percent by weight sio 54-66 A1203 17-27 MgO 4-12 CaO l0 BaO 0- 1 3,0,- 0-3 13 2 0 0-; Nag -l-K O 014 with powder-like additions of Percent by weight in the form of lithium carbonate (Li 'CO lithium aluminate (LiAlO 3,380,838 Patented Apr. 30, 1958 ice 2 lithium metasilicate (Li SiO magnesium oxide (MgO) magnesium oarbonate (MgCO magnesium silicate (MgSiO aluminum nitrate (Al(NO Percent by weight sio 54.50 A1203 2-6.40 CaO 10.00

B203 2.90 Na O 0.30 K20 0.10

BaO 0.90

MgO 4.60 F 0.30

As a sealing material for quartz goods and quartz glass a powder mixture has proven suitable which consists of 72% by weight of the glass powder of the above composition and 6.40 vpercent by weight Li O, 21.60 percent by weight A1 0 in the form of lithium aluminate.

A powder mixture which according to the invention meets the requirements for sealing and coating substances I to be used in connection with molybdenum, sintered corundum and cordierite ceramics consists of 71.50 to 86.00% by weight of the glass powder of the above composition and 14.00 to 28.50% by weight of magnesium oxide. Such substances are used in the manufacture of spark plugs.

For coating and insulating substances for metallic heat conductors consisting of 30% chromium, 5% aluminum and iron the powder mixture according to the invention contains 57% by weight of the aforedisclosed glass powder and 43% by weight of MgO.

The powder mixtures when used according to the invention are not sintered in known manner to dense articles, but the unsintered starting mixtures, or starting mixtures which were presintered to about 1000 Celsius and then were crushed again, are mixed with varying amounts of organic binding agents which can easily be eliminated again by burning, such as oils, turpentine, amylacetate with added nitrocellulose, and the like, and these compositions are ground to a pasty or a thin sprayable consistency depending on their intended use.

Sealing cements for quartz goods and quartz glass products land for the various porcelain and ceramic masses are most efiicient in the form of a paste, while for the substance used for producing a protective coating, particularly on metals and metal alloys, a spraya ble condition is most advantageous. The pasty sealing substance is deposited by hand in a thin layer between the parts to be joined together, whereas the coating layers are applied either by dipping or by means of spray guns as is customary in the enamel industry. The burning of the layers for the purpose of achieving a mechanically firm and dense connection with the carrier is done in the 'same fashion as in the manufacture of glazes and glaze enamels of the coatings according to the invention, for example the coils of a metallic electric heat conductor may be arranged closely adjacent to each other without causing a short circuit. It is obvious that this results in a considerin well ventilated electric furnaces by gradually increas- 5 ably higher heating effect per cubic unit.

ing the temperature until the baking temperature is If e.g. pieces of quartz glass or quartz bodies are to be reached, whereby the organic binding agent burns out, fused together with the aid of powder mixtures accordand keeping this temperature constant for one half hour ing to the invention, at first a glass has to be manufacto three hours. Protective coatings on heat conductors tured having the following composition:

gay advantageously be applied or fused to the heat con- 10 Percent by Weight uctor by directly heating it electrically. 54 50 Depending upon the chemical nature of the inventive 2640 substances, the required baking temperatures will lie be- IOOO tween ll50 to 1250 C. After the baking process the Ca layers in contrast to the glazes and glaze enamels are 5 3 6 not vitreous but predominantly crystalline. This accounts g also for the fact that such layers in actual continuous use may be heated to l200 to 1450 C. without being Ba damaged. The operating temperatures of the layers are Mgo controlled by the melting points of the different crystals F u of which the layers are composed. The melting process for the manufacture of these During the burning process the plasticity of the glass glasses differs in nothing from the conventional methods; component effects first the wetting and adherence to the thus it does not represent any peculiarities for the specarrier. Thereupon, during the subsequent period of bakcialist. ing for one half hour to three hours at the required Of the glass obtained in this way, 72 g. are pulverized temperature a chemical reaction of the glass component to a granulation of 60 and mixed with 28 g. of pulverwith the added inorganic compound of the mixture takes ized lithium aluminate. This mixture is crushed with 80 place. to 100 g. of an aqueous ethyl-alcohol solution of about For obtaining mechanically durable sealings of the 50% by volume in a ball mill. After that, the crushed madescribed substances with the various sealing partners 30 terial is transformed by evaporation under constant stirit is necessary that the linear coefficients of thermal ring into a dry substance on an electrical sand bath. Acexpansion of both partners be adapted to one another as cording to the degree of viscosity desired, the dry powder far as possible within a wide temperature range, because mixture thus obtained is transformed with more or less then the mechanical tensions which arise during the sealamyl acetate in a mortar or in a ball mill into a paste ing process betveen the two partners can be kept low, until it is completely free from nodules. It is convenien thus assuring a good durability. to add to the amyl acetate 3% of nitrocellulose as a bind- The aforedescribed substances in the temperature range ing agent. of 20 to 300 C. and of to 800 C., respectively, have The powder transformed into a paste has to be stirred a linear coefiicient of thermal expansion of 20 to thoroughly before use and spread in a uniform layer 107- 10- C. This means that the mixtures according to 40 thickness on the quartz substratum to be fused. The seethe invention provide sealing substances and coating layond quartz piece is then slightly pressed on the first one, ers which are suitable for a multitude of temperature reso that there remains yet a coherent, uniform intermedisistant materials of different coefficients of thermal expanate layer of the paste. The paste pressed out from between sion, such as quartz goods, quartz glass, porcelain and the two quartz pieces can be removed or flattened by ceramic masses, metals and metal alloys. means of a brush.

The appended table shows the melting points and linear At room temperature the solvent evaporates in about coelficients of thermal expansion or (from Jahrbuch fiir 30 minutes. The binding agent contained in the paste fixes Keramik-Glas-Ernail 1954/55, page 183 ff.) of the differthe quartz pieces to each other. The sample is heated up ent crystal structures which after the baking process are r in air, starting from room temperature. Up to 500 C. contained in the substances according to the invention. the rate of heating up must not be inferior to %1 hour,

Baked-on layers of the inventive mixtures possess also in order to slowly remove the organic binder; the further an excellent electric insulating property which makes heating up to 1l801200 C. may be effected at any them valuable in two respects. Firstly, the inventive coatspeed in a conventional furnace. ings are able to stop effectively the more or less strong For fusing together, 1180-1200" C. are indispensable. oxidation of almost all metals and metal alloys in the air This temperature is maintained for 30 minutes; afterat temperatures over 1000 C. This is of particular imwards the fused sample may be taken out of the furnace; portance for the industrial application of the metals tungit is, however, more convenient to cool it down in the sten, molybdenum, niobium and tantalum and their alfurnace.

TABLE Melting Point aX 0 Crystal Structure in Celsius n 20-300)/ o. (20n00)/ C. (20-700")/ o. (20-1200 o.

Spodrrrneno, LizO-AlgO3-4Si0g 1, 430 5 Eucr'yptite, nno-nrzoi-zsron 1, 380 Anorthite, CaOAlZO -ZSiOZ 1. 550 43 Cordierite, 2 MgO-2Al2O3-5SiOz 11 Spinal, MgO-AlgO 2,135 Forsterite, ZMgO-SiO; 1, S -112 Lithiumalunrinat, LlQO -Alz03 I 1 Strong contraction. 2 Decomposition at 1,460 into mullit-l-glass compoum l. 3 Sinter temperature of components at 1,500". From M. Mehmel, Lithiurnaluminum silicates as ceramic raw materials, Glas-En1ail-Keramo-Technik,

No. 9, Sept. 1959, pp. 337/340.

loys which moreover are gaining an increasing significance in the construction of airplane motors and turbines.

What I claim is: 1. A powder mixture which is to be heated and sintered Secondly, owing to the high electric insulating property 75 for producing crystalline, heat resistant coatings for quartz goods, quartz glass. porcelain, ceramics, metals and metal alloys, said powder mixture consisting of variable percentages by weight of a high-alumina glass powder having the following composition range:

Percent by weight SiO 54-66 A1 0 17-27 MgO 4-12 CaO 0-10 BaO 0-1 n TiO 0-3 F 0-0.3

Na O-I-K O 04 and powder-like additions of A1 0 0-22 Li O 012 MgO 4-55 SiO 0-10 selected from the group of lithium carbonate (Li CO lithium aluminate (LiAlO lithium metasilicate (Li SiO magnesium oxide (MgO) magnesium carbonate (MgCO magnesium silicate (MgSiO and aluminum nitrate (Al(NO 2. A powder according to claim 1, in which the glass powder has the following composition:

Percent by weight SiO 54.50 A1 0 as 26.40 CaO 10.00 B 0 2.90 Na O 030 K 0 0.10 BaO 0.90 MgO 4.60 F 0.30

3. A powder mixture for producing crystalline, heat resistant coatings for quartz goods, quartz glass, porcelain, ceramics, metals and metal alloys, in which 72% by weight of a glass powder having the following composition:

Percent by weight SiO 54.50

A1203 26.40 CaO 10.00 13203 2.90

Percent by weight Na O 0.30 K 0 0.10 BaO 0.90

MgO 4.60 F 0.30

is mixed with 6.4% by weight Li O and 21.6% by weight A1 0 in the form of lithium aluminate to constitute a sealing substance for quartz goods and quartz glass.

4. A powder according to claim 1, in which 71.5 to 86% by weight of a glass powder having the following composition:

Percent by weight is mixed with 14 to 28.5% by weight of MgO to form a coating substance for molybdenum, sintered corundum and cordierite ceramics.

5. A powder according to claim 1, in which 57% by weight of a glass powder having the following composition:

Percent by weight SiO 54.50 A1 0 26.40 CaO 10.00 B 0 2.90 Na O 0.30 K 0 0.10 BaO 0.90 Mg 4.60 F 0.30

is mixed with 43% by weight of MgO to form an insulating coating for metallic heat conductors including 30% chromium, 5% aluminum and iron.

References Cited UNITED STATES PATENTS 3,246,972 4/1966 Smith 106-39 2,848,349 8/1958 Rechter et a1. 117-129 2,920,971 1/1960 Stookey 106-39 3,037,828 6/1962 Michael 10648 X 3,148,994 9/1964 VOss 10652 X HELEN M. MCCARTHY, Primary Examiner. 

